Aalborg Universitet
10 years After The Largest River Restoration Project In Northern Europe
Kristensen, Esben; Kronvang, Brian; Wiberg-Larsen, Peter; Thodsen, Hans; Nielsen, Carsten
Brian; Amor, E.; Friberg, Nikolai; Pedersen, Morten Lauge; Baattrup-Pedersen, Annette
Published in:
Ecological Engineering
DOI (link to publication from Publisher):
10.1016/j.ecoleng.2013.10.001
10.1016/j.ecoleng.2013.10.001
Publication date:
2014
Document Version
Early version, also known as pre-print
Link to publication from Aalborg University
Citation for published version (APA):
Kristensen, E., Kronvang, B., Wiberg-Larsen, P., Thodsen, H., Nielsen, C. B., Amor, E., ... Baattrup-Pedersen,
A. (2014). 10 years After The Largest River Restoration Project In Northern Europe: Hydromorphological
changes on multiple scales in River Skjern. Ecological Engineering, 66, 141-149. [16]. DOI:
10.1016/j.ecoleng.2013.10.001, 10.1016/j.ecoleng.2013.10.001
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Contents lists available at ScienceDirect
Ecological Engineering
journal homepage: www.elsevier.com/locate/ecoleng
10 years after the largest river restoration project in Northern Europe:
Hydromorphological changes on multiple scales in River Skjern
E.A. Kristensen a,∗ , B. Kronvang a , P. Wiberg-Larsen a , H. Thodsen a , C. Nielsen a ,
E. Amor a , N. Friberg a , M.L. Pedersen b , A. Baattrup-Pedersen a
a
b
Aarhus University, Department of Bioscience, Silkeborg, Denmark
Aalborg University, Department of Civil Engineering, Aalborg, Denmark
a r t i c l e
i n f o
Article history:
Received 26 February 2013
Received in revised form 22 August 2013
Accepted 7 October 2013
Available online xxx
Keywords:
River restoration
Long-term
Physical condition
Floodplain
Low-land rivers
a b s t r a c t
The lower river Skjern (Denmark) historically contained a large variation in habitats and the river ran
through large areas with wetlands, many backwaters, islands and oxbow lakes. During the 1960s the
river was channelized and the wetland drained. A restoration during 2001–2002 transformed 19 km of
channelized river into 26 km meandering river. The short-term effects of this restoration have previously
been reported and for this study we revisited the river and with new data evaluated the long-term (10
years) hydrological effects of the restoration. The evaluation was done on three different scales: (1) instream habitats, (2) channel stability and (3) re-connection with the floodplain. In-stream habitats had
changed little over the past 10 years and the habitats today showed close similarity with the habitats
recorded immediately after the restoration. Measurements of channel stability showed that erosion and
sedimentation have changed the cross-sectional profiles over the last 10 years, resulting in a net input of
sediment to the lower reaches of the river. However, the change of channel form was a slow process and
predicted bank retreat over a 100 year period was only up to 6.8 m. Hence the formation of lost habitats
(islands, backwaters and oxbow lakes) is a very slow process and the spontaneous development of these
habitats will take centuries. Furthermore, the evaluation also showed that the restoration re-connected
the river with its floodplain and large areas of riparian areas are today periodically flooded, but that
the flooding is controlled and tamed due to the restoration design. The restoration of River Skjern has
therefore failed to re-create the natural habitats formerly present and the natural dynamic processes that
shape these habitats are slow. To speed up this process we therefore recommend restoration engineering
using a natural guiding image when restoring lowland rivers in the future and through this restoring the
lost habitats and the dynamic processes characteristic of natural rivers.
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
Habitat degradation is a serious threat to biodiversity (Dobson
et al., 1997; Vitousek et al., 1997; Wilcove et al., 1998) and aquatic
ecosystems are among those most severely impacted (Allan and
Flecker, 1993; Sala et al., 2000). Over centuries, streams, rivers and
their floodplains have been modified (e.g. Sparks, 1995; Kronvang
et al., 1998; Bernhardt et al., 2005) as a result of land drainage,
flood plain urbanization, flood defence and navigation (European
Environment Agency, 1998). In North-western Europe, modification and channelization of watercourses have been particularly
extensive and have left less than 10% of lowland streams in Great
∗ Corresponding author at: Aarhus University, Department of Bioscience,
Vejlsøvej 25, DK-8600 Silkeborg, Denmark. Tel.: +45 87158753.
E-mail address: [email protected] (E.A. Kristensen).
Britain, the Netherlands and Denmark in their natural physical
state (Brookes and Long, 1990; Verdonschot and Niiboer, 2002).
Thus, extensive damage has been caused to the river ecosystems
with a widespread loss of habitats for biota, and the biodiversity of
European rivers and floodplains is today significantly reduced.
As a consequence of the widespread damage to stream and
river ecosystems, and based on a growing recognition of the conservation values within them, the number of river restoration
projects has increased substantially in recent years (Bernhardt
et al., 2005). River restoration efforts have primarily focused on
channel re-configuration, and in-stream habitat improvements
increasing heterogeneity, by re-meandering and adding physical
structures such as wood, boulders and artificial riffles (e.g. Larson
et al., 2001; Kasahara and Hill, 2008; Miller et al., 2010). However, during the last 10 years there has been a growing scientific
and management-oriented recognition of the importance of restoring the natural processes of river ecosystems (Williams, 2001;
0925-8574/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ecoleng.2013.10.001
Please cite this article in press as: Kristensen, E.A., et al., 10 years after the largest river restoration project in Northern Europe: Hydromorphological changes on multiple scales in River Skjern. Ecol. Eng. (2013), http://dx.doi.org/10.1016/j.ecoleng.2013.10.001
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Kondolf et al., 2006). This paradigm shift has resulted in a transition
from small-scale engineering-dominated restoration approaches
toward catchment-scale approaches that focus on enhancing both
in-stream habitats and re-connection of the river with its floodplain and through this restoring freshwater wetlands (Hillman and
Brierly, 2005; Kondolf et al., 2006). Therefore, there is a need to
focus on the entire freshwater ecosystems including the riparian
wetlands and through this the restoration of ecosystem processes
and functioning which is vital to sustain the services these systems
provide (Loomis et al., 2000). Scientific evaluations of catchmentscale restoration projects are however rare, especially studies that
monitor the long-term responses (Friberg et al., 1998; Feld et al.,
2011). Long-term evaluations are highly relevant as such studies
can help us to advance the science of river restoration (Wohl et al.,
2005) and ultimately help us achieve a higher rate of restoration
success (Palmer et al., 2005).
The overall aim of this study was to evaluate the longer-term
effects of restoring River Skjern, Denmark. This restoration project
is the largest river restoration project in Northern Europe to date,
aiming to enhance the nutrient retention capacity of the river by
re-creating a natural hydrology in the river valley including reconnection of the river and the riparian wetlands and to enhance
biodiversity by restoring the physical and hydrological dynamics of
the river and the floodplain (Pedersen et al., 2007a). River Skjern is
located in Western Denmark and drains a catchment of 2490 km2 .
Land use in the catchment is dominated by agriculture and the
geology of the area is a combination of sandy outwash plains and
mostly sandy moraines (Smed, 1982). The river has the highest discharge of any Danish rivers (annual mean 35 m3 /s) why the river is
of high regional importance as a biodiversity hotspot (Ovesen et al.,
2000; Andersen et al., 2005). From historical maps dating back to
the 1800th century the lower 10 km of the river can be classified as
anastomosing with numerous channels between low relatively stable vegetated islands (Miall, 1977; Richards, 1997). During the late
1960s the lower 19 km of the river was channelized and riparian
wetlands were drained as a result of increasing demand for agricultural production. River channelization and drainage was at the
time considered a prerequisite condition for agricultural growth
in the Danish society. However, 25 years later the area had lost
its agricultural value and in 1987 the Danish government initiated plans to restore the area. The restoration was conducted in
2000–2002 and resulted in the transformation of the lower 19 km
of channelized river into 26 km of meandering river (Pedersen
et al., 2007a). The short-term effect of the restoration on in-stream
habitats, macrophytes and macroinvertebrates has previously been
reported (Pedersen et al., 2007b), however, the longer-term effects
are unknown. The aim of this study was therefore to re-visit the
River Skjern and analyze the development in channel morphology and habitats 10 years after the completion of the restoration.
We investigated morphological development using three different spatial scales: (1) in-stream habitats, (2) channel stability and
(3) the re-connection of the river with its riparian wetlands. We
hypothesized that significant changes have occurred during these
10 years and that the River Skjern has developed into a river system
with near-natural hydromorphology. The term hydromorphology
is used as defined by Ŝípek et al. (2009), for discussion see Vogel
(2011).
2. Methods
2.1. In-stream habitats
The short-term effects of the restoration on in-stream habitats
have previously been evaluated in three 300 m long reaches along
the restored River Skjern (R1, R2, R3, Fig. 1) based on a comparison with a 300 m long control reach (C, Fig. 1) located upstream
of the restoration area (Pedersen et al., 2007b). All four reaches
was sampled once before the restoration (2000) and again immediately after the restoration (2003; Pedersen et al., 2007b). After
the restoration the location of R2, R3 and C remained at the same
location as pre-restoration, while, as a results of the restoration
and filling-up of major parts of the channelized river, reach R1 was
in 2003 moved from the northern drainage channel to the newly
excavated river channel located app. 2 km south (Fig. 1). For this
study, we re-sampled these four reaches in 2011 providing data
for a long-term evaluation (app. 10 years) of the restoration on instream habitats. Identical surveying methods were used in all three
years to allow for cross-year comparison, for a detailed description
of the methodology, see Pedersen et al. (2007b). In brief, six transects were placed equally spaced along each of the four reaches
and each transect was divided into 1 m × 1 m quadrats across the
entire width. A GPS was used to exactly identify location of each
transect. At each quadrat, depth (to nearest cm), current velocity (at 10 cm above the stream bed), dominating substrates (using
seven categories according to the Wentworth-scale (Wentworth,
1922) and macrophyte coverage (%) was recorded. Recording of instream variables was done in September 2000, August 2003 and
September 2011 and it was aimed to collect data at similar discharge levels. However, the summer 2003 was drier than normal
and mean monthly discharge for August 2003 was 12.7 m3 /s, while
mean monthly discharge for September 2000 and September 2011
was 19.4 m3 /s and 19.1 m3 /s, respectively.
To evaluate the long-term changes to in-stream habitats we
divided the recordings from each transect into two groups two
groups termed a “Vegetated zone” and a “Main current zone”.
The first group was defined as quadrats with depths from 0 to
130 cm, often located along the edges of the river channel supporting vascular macrophytes, as these rarely occur at depths larger
than 130 cm. The second group was quadrats with depths larger
than 130 cm, often located in the mid-channel and being without
vascular macrophytes. We preformed this a priori separation of
the data to obtain a river-zone-specific evaluation of the physical
changes during the 10 year period because these two main channel
zones are expected to form different in-stream habitats for plants,
macroinvertebrates and fish. For this study, we calculated a number of in-stream parameters using the transect data recorded in
2000, 2003 and 2011. For each transect, we calculated Coefficients
of Variation (CV) for depth, mean current velocity and mean macrophyte coverage separate for the two habitat zones. In addition, we
used substrate recording to calculate percent occurrence of four
substrate types (peat, mud, sand and gravel) and produced transect
means for each substrate type separately for the two zones. Finally,
we used three different variables (domination, diversity and score)
to describe changes in substrate for each transect divided into
the two zones according to O’Hare et al. (2006). A value between
1 and 4 was allocated to the four substrate categories with values increasing with particle size. Domination was defined as the
dominant substrate, i.e. the category occurring in most quadrats,
diversity was the number of categories occurring and score the
weighted average of the categories present in each transect. All
physical variables used to evaluate changes to in-stream habitats
for the four reaches and the two different zones are summarized in
Table 1.
To investigate the effect of the restoration on in-stream habitats
and the long-term development in the habitats we preformed
Principal Response Curve analyses (PRC, Van den Brink and Ter
Braak, 1999). The analyses were done with year 2000 as reference
points (Van den Brink et al., 2009) thus enabling us to investigate
the change of in-stream habitats relative to the physical condition
Please cite this article in press as: Kristensen, E.A., et al., 10 years after the largest river restoration project in Northern Europe: Hydromorphological changes on multiple scales in River Skjern. Ecol. Eng. (2013), http://dx.doi.org/10.1016/j.ecoleng.2013.10.001
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Fig. 1. Map showing the study area, study sites for in-stream habitats (R1, R2, R3 and C), and the position of transects used to measure channel stability (1–66).
before the restoration. All analyses were done using R (version
2.15, R Core Team, 2012) and we performed the analyses separately for each of the four river reaches and separately for the
two different habitat zones. The PRC analyses with year 2000
as a fixed reference point were performed in a series of steps.
First we calculated a Redundancy Analysis (RDA) using the RDA
function (vegan package). All in-stream variables (Table 1) were
z-standardized prior RDA. We then extracted the scores of the first
RDA axis for each transect, calculated mean RDA scores for each
year and calculated the difference in mean RDA scores between the
reference year (2000) and years 2003 and 2011. This difference in
RDA scores was then plotted against time to produce the final PRC
Table 1
Physical variables (mean with range) included in the analysis of in-stream habitats for the vegetated zone (a) and the main current zone (b). See text for further explanations.
R1
R2
R3
C
(a)
CV depth
Current velocity (m/s)
Macrophyte coverage (%)
Peat (%)
Mud (%)
Sand (%)
Gravel (%)
Dominance substrate
Diversity substrate
Score substrate
0.36 (0.13–0.64)
–
78 (14–132)
4 (0–30)
22 (0–53)
74 (30–100)
(0–8)
2.8 (2–3)
2.1 (1–4)
271 (200–300)
0.31 (0.06–0.68)
25 (2–37)
47 (0–108)
0.01 (0–0.01)
18 (0–87)
78 (13–100)
3 (0–40)
2.8 (2–3)
1.6 (1–2)
284 (213–340)
0.42 (0.13–0.70)
30 (2–51)
57 (0–143)
0.01 (0–0.01)
13 (0–66)
79 (16–100)
7 (0–77)
2.9 (1–4)
1.8 (1–3)
292 (250–377)
0.41 (0.05–0.83)
–
132 (0–260)
0.01 (0–0.01)
23 (0–67)
67 (33–100)
9 (0–51)
2.8 (2–3)
1.7 (1–3)
285 (233–350)
(b)
CV depth
Current velocity (m/s)
Macrophyte coverage (%)
Peat (%)
Mud (%)
Sand (%)
Gravel (%)
Dominance substrate
Diversity substrate
Score substrate
0.08 (0.01–0.14)
–
28 (0–140)
0.4 (0–5)
2 (0–7)
95 (75–100)
3 (0–17)
3 (3)
1.8 (1–4)
300 (294–313)
0.06 (0.03–0.11)
–
6 (0–20)
0
2 (0–7)
93 (60–100)
5 (0–40)
3 (3)
1.5 (1–2)
303 (293–340)
0.06 (0.01–0.15)
38 (25–54)
14 (0–46)
0
0
73 (0–100)
27 (0–100)
3.3 (3–4)
1.4 (1–2)
327 (300–400)
0.07 (0.02–0.12)
35 (27–46)
13 (0–28)
0.01 (0–0.01)
1.4 (0–7)
84 (72–95)
15 (0–28)
3 (3)
2.1 (2–3)
314 (300–328)
Please cite this article in press as: Kristensen, E.A., et al., 10 years after the largest river restoration project in Northern Europe: Hydromorphological changes on multiple scales in River Skjern. Ecol. Eng. (2013), http://dx.doi.org/10.1016/j.ecoleng.2013.10.001
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Fig. 2. Principal response curve analyses of the development of in-stream habitat parameters in four different sites of the vegetated zone (depths 0–130 cm) of River Skjern:
control upstream the restored reaches (R1, R2, R3).
plot. Current velocities (v10) were not measured in the vegetated
zone of the control reach and both zones of R3 why the analysis
were performed without this variable for these. Following PRC
analyses we used one-way ANOVA’s to test for a significant effect
of year. We used the RDA scores for each transect of the first
axis for 2000 and the difference in scores between the reference
year (2000) and years 2003 and 2011 in the ANOVA’s. When the
global one-way ANOVA was significant, we used Tukey pair-wise
comparisons to compare years.
2.2. Sedimentation and erosion
To study the stability of the restored river channel and investigate how sedimentation and erosion affects the cross-sectional
profile of the river, 65 transects were surveyed along the lower
10 km of the river (Fig. 1). Detailed measurements of these 65 crosssections were performed immediately after the restoration (in
2001) and again in 2011. All cross sections were surveyed using RTK
GPS equipment with a vertical error <20 mm (Leica Geosystems,
2010) and for each year x, y and z coordinates were obtained for
20 points per transect. After measurements all data points were
transformed into profile lines. Erosion and sedimentation volumes
were then calculated for each transect as the difference in height
of the riverbed (z coordinate). Calculations were done separately
for three cross-sectional compartments: (i) the left bank, (ii) the
right bank and (iii) the river bed. The erosion and sedimentation
was estimated as both a gross and a net amount and to determine the erosion and sedimentation between two consecutive
transects we used nearest neighbor interpolation. In addition, we
calculated bank retreat for both left and right bank for each transect.
2.3. Re-connection with the floodplain
To study the connectivity between the River Skjern, and its surrounding riparian areas river, water levels were modeled using
the one dimensional hydraulic model MIKE11 (DHI, 2011). The
hydraulic model was based on trans-sectional profiles no. 1–33
(Fig. 1) measured in 2001. The upstream model boundary was based
on measured daily river flows covering the period 2001–2011
(Ovesen et al., 2000) and the downstream model boundary was
based on sub-daily measurements of sea surface water levels at
Bork Harbor located 9 km south west of the river outflow. The
model was calibrated against measured water levels by adjusting
a time series of daily Manning M numbers calculated at the most
downstream permanent river flow gauging station on the River
Skjern (Thodsen et al., 2006). When the modeled water levels were
higher than the river banks the extent of the flooding was estimated
based on a 1.6 m resolution LIDAR DEM (KMS, 2010) and the combined flooded area were calculated. Riparian wetland areas being
flooded were estimated based on the 90th flow percentile in the
river during the period 2001–2011.
3. Results
3.1. In-stream habitats
When comparing RDA scores, we found no significant overall
change to in-stream habitats in the vegetated zone of the control
reach from 2000 to 2003 (P = 0.493; Fig. 2) however, from 2003 to
2011 there was a significant change (P = 0.0008; Fig. 2). This change
was primarily caused by an increase in CV Depth, indicating more
heterogeneous stream profiles with larger variation in depth in
Please cite this article in press as: Kristensen, E.A., et al., 10 years after the largest river restoration project in Northern Europe: Hydromorphological changes on multiple scales in River Skjern. Ecol. Eng. (2013), http://dx.doi.org/10.1016/j.ecoleng.2013.10.001
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Fig. 3. Principal response curve analyses of the development of in-stream habitat parameters in four different sites of the current zone (depths >130 cm) of River Skjern:
control upstream the restored reaches (R1, R2, R3).
2011 compared to 2003. In the vegetated zone of R3 and R2 the
restoration resulted in a significant change to in-stream habitats
(P = 0.022 and P = 0.026, respectively). In this zone of R3, the restoration resulted in higher current velocities (v10), a coarser substrate
(Score substrate) although still dominated by sand, a higher coverage of gravel, a reduction in coverage by mud and consequently
a lower substrate diversity (Fig. 2). In the vegetated zone of R2,
the restoration also resulted in increased current velocities (v10),
a coarser substrate (Score substrate) although still dominated by
sand, a relatively higher coverage of gravel, lower coverage of mud
and a lower substrate diversity (Fig. 2). In addition, the analysis
showed that the overall significant changes to in-stream habitats
of the vegetated zone of R3 were also related to a reduction in
macrophyte coverage (Fig. 2).
The observed changes to in-stream habitats in the vegetated
zone of R3 and R2 were stable over time showing no change from
2003 to 2011 (P = 0.906 and P = 0.722; Fig. 2). The in-stream habitats
of the vegetated zone in the most downstream reach (R1) was not
significantly affected by the restoration as only very small changes
occurred from 2000 to 2003 (Fig. 2). From 2003 to 2011 there was
some development in in-stream habitats but these changes were
not significant (P = 0.897; Fig. 2).
Similar to the vegetated zone, we found no significant overall
change to in-stream habitats in the main current zone of the control
reach from 2000 to 2003 (P = 0.460; Fig. 3) and a small but significant change from 2003 to 2011 (P = 0.011; Fig. 3). This change was
primarily driven by an increase in CV depth, macrophyte coverage
and substrate diversity over the period (Fig. 3). In the main current
zone of R3 and R1, the restoration resulted in a significant change to
in-stream habitats (P = 0.02 and P = 0.011 respectively; Fig. 3), primarily caused by a higher variation in depth (CV depth) and higher
coverage by gravel and consequently a higher substrate score, a
higher substrate dominance score and a higher substrate diversity
(Fig. 3). As found for the vegetated zone of R3 and R1, the observed
changes to in-stream habitats following restoration, stayed stable
over time in the main current zone of R3 and R1 (P = 0.161and
P = 0.897, respectively; Fig. 3). No analysis was performed for R2
for the main current zone as only very few quadrates had depths
over 130 cm.
3.2. Sedimentation, erosion and bank retreat
The survey of 65 cross-sectional transects along the lower 10 km
of River Skjern in 2001 and again in 2011 revealed marked morphological adjustments through erosion and sedimentation in the
newly restored stream channel (Fig. 4). There was large variations in the morphological adjustments among transects during
the 10 year period (Fig. 5). Average sedimentation and erosion volume (±SD) measured at the left bank amounted to 231 ± 360 m3
and 274 ± 325 m3 , respectively, resulting in a net erosion of 43 m3
sediment. For the right bank, average sedimentation and erosion
volume (±SD) was 192 ± 340 m3 and 536 ± 740 m3 , respectively,
yielding a net erosion of 344 m3 sediment. However, the most pronounced morphological changes were observed at the river bed.
Average sedimentation (±SD) for this part of the cross-sectional
transects was 2259 ± 2333 m3 sediment and average erosion (±SD)
was 707 ± 996 m3 resulting in a net sedimentation of 1552 m3 sediment. Combined, the net balance resulted in a gain of 1166 m3
Fig. 4. Example of cross-sectional adjustments of the River Skjern between 2001
and 2012.
Please cite this article in press as: Kristensen, E.A., et al., 10 years after the largest river restoration project in Northern Europe: Hydromorphological changes on multiple scales in River Skjern. Ecol. Eng. (2013), http://dx.doi.org/10.1016/j.ecoleng.2013.10.001
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Fig. 5. Erosion and sedimentation in the lower 10 km of the restored River Skjern over a 10 year period (2001–2011).
sediment over the 10 years in the restored river channel. The net
result is a slightly wider and shallower river in 2011 than in 2001.
There was large variation in bank retreat among transects
(Fig. 6) and average bank retreat for left banks was 39 cm and
68 cm for right banks. This corresponds to a forecasted bank retreat
of 3.9 m for left banks and 6.8 m for right banks over a 100 years
period.
3.3. Re-connection with the floodplain
Before the restoration the channelized river had very little or
no connection with the floodplain due to protection of the adjacent agricultural areas with dikes along the river channel and
extensive drainage through pumping stations and ditches. The
restoration immediately re-connected the river with the floodplain
and based on the 2001 survey of the river channel cross-sections
the MIKE11 hydraulic model revealed that 611 ha riparian areas
located between transect 1 and 33 (Fig. 1) were flooded for 10%
of the period (2001–2011). The modeling also revealed that flooding was most pronounced during winter as there was connection
between the river and the floodplain for 30.5% and 25.2% of January
and February, respectively. During summer months flooding was
very rare and occurred for less than 1% of May, June, July and August.
4. Discussion
Evaluating the success of river restoration projects is often made
impossible due to the lack of both pre- and post-monitoring data
(Kondolf and Micheli, 1995; Lake, 2001; Palmer et al., 2005). This
lack of data has for decades hampered progress in our scientific and
practical understanding of what defines a successful river restoration project. The restoration of River Skjern is an exception to this
general rule as both pre- and post-monitoring data over shortand longer-term exist. These data therefore provides us with the
opportunity to evaluate and analyze success and use the results
to improve future river restoration projects. However, the lack of
monitoring data is not the only reason halting our understanding of river restoration success. Another important factor is the
lack of agreed criteria for judging success (Palmer et al., 2005).
The restoration of River Skjern was no exception and restoration
goals concerning hydromorphology were vaguely defined as the
aim to “restore the physical and hydrological dynamics of the river
and floodplain” (Pedersen et al., 2007a). We therefore choose to
evaluate the hydromorphological outcome of the restoration on
multiple scales in order to effectively determine if the restoration
had allowed for a more dynamic and natural river.
4.1. In-stream habitats
We found immediate changes to in-stream habitats following
restoration and there were significant differences at reach-scale instream habitats between 2000 and 2003 for most of the restored
reaches and for both habitat zones – primarily due to increase in
current velocity (through narrowing of the channel) and addition
of coarse sediment during restoration. The channelized stream had
been constructed in order to secure effective drainage of agricultural areas and the channel was therefore wide and very straight.
Consequently, the variation in depth was relatively small. The
restoration decreased the width of the stream channel and consequently increased current velocity. The only reach where the
Please cite this article in press as: Kristensen, E.A., et al., 10 years after the largest river restoration project in Northern Europe: Hydromorphological changes on multiple scales in River Skjern. Ecol. Eng. (2013), http://dx.doi.org/10.1016/j.ecoleng.2013.10.001
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the time spand of our evaluation would probaply require more
dynamism than is possible at the moment. This is primarilly due
to the lack of large structuring elements (e.g. large woody debris;
LWD) in the river – elements that can be transported downstream
and create erosion of banks and streambed and consequently
change the habitats. The question is therefore if the restoration of
the lower River Skjern has created an artificially stable condition
that leaves little room for the dynamics that forms natural rivers
and creates habitats for a large variety of flora and fauna? Definitive
answers to this question are difficult due to the relatively short time
span of our evaluation however, it is very likely that increasing the
occurrence of LWD in the rivers would increase the dynamism of
the river. This would require a change to the current management
strategy of Danish rivers where LWD are removed from the channels. Furthermore, it is importance to acknowledge the fact that we
performed a transect-scale analysis of the long-term development
in physical conditions. Had we done the evaluation on a smaller
scale (e.g. quadrate-scale or microhabitat scale) temporal changes
would most likely have been larger as temporal dynamics increase
with decreasing spatial scale (Frissell et al., 1986).
4.2. Sedimentation, erosion and bank retreat
Fig. 6. Bank retreat in the lower 10 km of the restored River Skjern over a 10 year
period.
restoration did not have an immediate impact on in-stream condition was the reach located most downstream (R1). At this reach, the
restoration only decreased average transects width from 47.7 m to
45.7 m (4% decrease), while the decrease in average width was 29%
and 17% for reaches R2 and R3, respectively. The addition of gravel
is a common restoration practice in Denmark (Pedersen et al., 2009;
Kristensen et al., 2011) and R2 and R3 also received gravel as part
of the restoration. Gravel was not added to R1 which together with
the limited reduction in width reflects the downstream location of
this reach. Excessive addition of coarse material and further narrowing of the stream channel would therefore not have been in
accordance with the natural river type for this location.
10 years after the restoration, we found that the in-stream habitats had gone through very little changes compared to the 2003
situation. The condition of all restored reaches was not significantly different from the condition created 10 years before. By
nature, rivers and river channels are temporally variable (Rosgen,
1996) and natural rivers are characterized by continuous changes
to channel form and habitats (Petts et al., 1995). These natural
structural processes are important for river biodiversity and biofunction (Elosegi et al., 2010) and therefore ultimately for the
ecological quality of rivers. However, defining the natural level of
dynamic hydromorphological processes in rivers are not easy (Sear
and Newson, 2003; Newson and Large, 2006) and relatively stable periods might be interspersed with periods of disturbance or
change. Large changes to in-stream habitats in River Skjern over
Immediately following restoration, the newly created stream
channel of River Skjern experienced marked morphological adjustments because of the unconsolidated state of the river bed and
banks (Pedersen et al., 2007b). This phenomenon has been reported
for other river restoration projects as well (e.g. Sear et al., 1998). The
present study has documented further morphological adjustments
to the channel and 10 years later erosion and sedimentation has
altered the cross-sectional profiles significantly. Along the investigated 10 km of river there was a surplus of sediment indicating a
decrease in bed sediment transport capacity compared to further
upstream. Over time the surplus of sediment and deposition along
the lower parts of the River Skjern will lead to increased flooding that potentially will erode flood channels that again potentially
could develop into permanent channels and recreate the formerly
existing anastomosing river planform. Furthermore, the surplus
of sediment can also over time lead to the formation of fluvial
islands – a habitat type that existed historically in the river. It must
be estimated that the time horizon of a new naturally developed
anastomosing river and fluvial islands pattern is long, probably
centuries. There are yet no safe indications on this development
being ongoing. In other river types (braided rivers) the formation
of islands occurs over 10–20 years (Gurnell et al., 2001) and is typically initiated when LWD lodges on a shallow section of the river
(Ward et al., 2002). The formation of islands process is probably
slower in lowland rivers and LWD is completely absent from most
Danish rivers (including River Skjern) as trees are often not allowed
to grow along river channels due to their extensive use for farming
and any wood are routinely removed through river maintenance
practices (Kristensen et al., 2012). Abandoning this practice and
allowing trees along rivers and LWD in the rivers would benefit
the creation of dynamic river channels (Gurnell et al., 2005) and
eventually speed up the formation of fluvial islands.
In general, is the dynamics of river channels dependent on
which scale the morphological changes occur (Frissell et al., 1986).
At small scale (e.g. sediment rearrangement), changes occur over
hours or days (Elosegi et al., 2010). Changes at a larger scale, such
as lateral migration of river channels that leads to meander cutoff and the formation of oxbow lakes can take centuries (Gilvear
and Bravard, 1996; Hooke, 2004). We measured the lateral migration rates (bank retreat) of River Skjern to be 3.9 cm/year and
6.8 cm/year for the left and right bank, respectively. Compared to
reported migration rates for another Danish river (River Odense)
Please cite this article in press as: Kristensen, E.A., et al., 10 years after the largest river restoration project in Northern Europe: Hydromorphological changes on multiple scales in River Skjern. Ecol. Eng. (2013), http://dx.doi.org/10.1016/j.ecoleng.2013.10.001
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the rate for River Skjern is relatively high (Kronvang et al., 2012)
but the rate is relatively low compared to lowland rivers from
other regions (Gilvear and Bravard, 1996). Meander cutoff and formation of oxbow lakes in the restored river can therefore not be
expected within the next centuries. Historical maps confirm that
oxbow lakes and fluvial islands were features of the lower River
Skjern before channelization and drainage however, these channel characteristic were not re-created during restoration (Pedersen
et al., 2007a). There has been extensive research on the roles of
channel complexity on biodiversity and ecosystem functioning (e.g.
Hutchinson, 1959; Beisel et al., 1998; Aldridge et al., 2009; Elosegi
et al., 2010) providing evidence for a positive relationship between
complexity and biodiversity. Given the extensive periods of time
needed before spontaneous re-formation of islands and oxbow
lakes in River Skjern and the fact that these features were present
historically, active re-creation of them during restoration would
have increased chances of ecosystem recovery. We did not include
biological samples in the current evaluation of the River Skjern
restoration however, it is likely that species inhabiting shallow and
slow-flowing areas (e.g. backwaters or oxbow lakes) have not made
a full recovery due to the scarcity of these habitats today.
4.3. Re-connection with the floodplain
The restoration of the lower River Skjern re-connected the river
with the floodplain and large areas are frequently flooded and some
areas are even permanently water filled (Andersen et al., 2005).
Especially the birdlife has responded positively to this change and
the number of breeding species in the area increased from 7 to
31 between 2000 and 2003 (Andersen et al., 2005) however, this
number has declined in recent years (Holm, T.E., unpublished data).
During flooding, the water delivers sediment to the floodplain
which contains seeds and the re-connection can therefore help
to increase the possibility of re-colonization by plant species to
the riparian areas (Baattrup-Pedersen et al., 2012). Furthermore,
flooding can also increase retention of phosphorous and nitrogen
(Baldwin and Mitchell, 2000; Kronvang et al., 2007) that otherwise would end up in the marine recipient and potentially cause
environmental problems. The benefits from re-connection of rivers
with their floodplain are therefore plentiful and there are many
more than the ones mentioned here (Tockner et al., 2000). However, the flooding along River Skjern does not follow a natural
pattern. It has previously been estimated that discharge in River
Skjern have to be above 40 m3 /s before the river is connected with
the floodplain (Andersen et al., 2005). This threshold value is a
consequence of a desire to limit water flow through riparian wetlands and the construction of the restored river channel therefore
included a designated in-flow area. This design was used to minimize the loss through predation of downstream migrating Atlantic
salmon smolts (Salmo salar) in the wetlands (Andersen et al., 2005).
However, this design limits the flooding frequency and the amount
of water that flow into the floodplain (Andersen et al., 2005). Furthermore, the limited connection probably also has consequences
for the morphological dynamics of the restored river channel as the
channel is fixed in places to maintain the design.
5. Conclusion
With this study we have highlighted the value of long-term
monitoring following river restoration and present data from an
evaluation 10 years after one of the largest river restoration projects
in Europe. Long-term monitoring is rare and this study therefore
provides us with a unique opportunity to improve our knowledge about restoration success (Palmer et al., 2005). We evaluated
the restoration on three different morphological scales (in-stream,
channel morphology and re-connection with the floodplain) and
how the morphology had hanged over the last 10 years. We found
that in-stream habitats had changed very little since the immediate change following restoration and that the relatively stable
stream channels were created during restoration. Along this line,
we also measured the dynamic processes shaping river channels
(erosion and sedimentation) and found that the rate of changes
are relatively slow and the spontaneous creation of lost habitats
(islands, backwaters and oxbow lakes) will take centuries. Moreover, although we found that the restoration had re-connected the
River Skjern with its floodplain, this re-connection was tamed and
controlled. If the aim of restoring River Skjern was to bring back the
lost habitats, and the flora and fauna associated with these, we can
therefore concluded that the restoration is not yet a success. Rivers
are dynamic and the processes that will shape the lost habitats are
slow and even within the scope of the present study (10 years),
which is relatively long-term, the success can therefore be evaluated. However, to speed up this process we recommend restoration
engineering using a natural guiding image when restoring streams
and rivers in the future and through this restoring the lost habitats and the dynamic processes characteristic of natural rivers. We
did not evaluate the biological recovery of River Skjern following restoration in the present study, but recently collected data
(Wiberg-Larsen, unpublished data) suggest that the many macroinvertebrate and macrophytes associated with islands, backwaters
and other slow-flowing areas have not returned to the restored
river – partly because the habitats have not been re-created. Only
when doing this we can expect a return of the lost species.
Acknowledgements
This study was funded by the 15. Juni Foundation and the EU
project REFORM. We wish to thank Sandra Hille for statistical
advice and Uffe Mensberg and Henrik Stenholt for assistance in
the field.
References
Aldridge, K.T., Brookes, J.D., Ganf, G.G., 2009. Rehabilitation of stream ecosystem
functions through the reintroduction of coarse particulate organic matter. Res.
Ecol. 17, 97–106.
Allan, D.J., Flecker, A.S., 1993. Biodiversity conservation in running waters. BioScience 43, 32–43.
Andersen, J.M., Jessen, K., Larsen, B.B., Bundgaard, P., Glüsing, H., Illum, T., Hansen,
L.B., Damgaard, O., Koed, A., Baktoft, H., Jensen, J.H., Linnemann, M., Ovesen, N.B.,
Svendsen, L.M., Bregnballe, T., Skriver, J., Baattrup-Pedersen, A., Pedersen, M.L.,
Madsen, A.B., Amstrup, O., Bak, B., 2005. Restoration of River Skjern (in Danish).
Scientific Report from NERI no. 531.
Baldwin, D.S., Mitchell, A.M., 2000. The effects of drying and re-flooding on the
sediment and soil nutrient dynamics of lowland river–floodplain systems: a
synthesis. Reg. Rivers: Res. Manag. 16, 457–467.
Beisel, J.N., Usseglio-polatera, P., Thomas, S., Moreteau, J.-C., 1998. Stream community structure in relation to spatial variation: the influence of mesohabitat
characteristics. Hydrobiologia 422, 163–171.
Bernhardt, E.S., Palmer, M.A., Allan, J.D., Alexander, G., Barnas, K., Brooks, S., Carr,
J., Clayton, S., Dahm, C.N., Follstad-Shah, J., Galat, D.L., Closs, S., Goodwin, P.,
Hart, D.D., Hassett, B., Jenkinson, R., Katz, S., Kondolf, G.M., Lake, P.S., Lave, R.,
Meyer, J.L., O’Donnell, T.K., Pagano, L., Powell, B., Sudduth, E., 2005. Ecology –
synthesizing US river restoration efforts. Science 308, 636–637.
Brookes, A., Long, A.J., 1990. Chart Catchment Morphological Survey: Appraisal
Report and Watercourse Summaries. National Rivers Authority Reding.
Baattrup-Pedersen, A., Dalkvist, D., Dybkjær, J.B., Riis, T., Larsen, S.E., Kronvang, B., 2012. Species recruitment following flooding, sediment
deposition and seed addition in restored riparian areas. Res. Ecol.,
http://dx.doi.org/10.1111/j.1526-100X.2012.00893.x.
DHI, 2011. MIKE 11 – A Modelling System for Rivers and Channels, Reference Manual. Danish Hydraulic Institute, pp. 536.
Dobson, A.P., Bradshaw, A.D., Baker, J.M., 1997. Hopes for the future: restoration
ecology and conservation biology. Science 277, 515–522.
Elosegi, A., Díez, J.R., Mutz, M., 2010. Effects of hydromorphological integrity on
biodiversity and functioning of river ecosystems. Hydrobiologia 657, 199–215.
Please cite this article in press as: Kristensen, E.A., et al., 10 years after the largest river restoration project in Northern Europe: Hydromorphological changes on multiple scales in River Skjern. Ecol. Eng. (2013), http://dx.doi.org/10.1016/j.ecoleng.2013.10.001
G Model
ECOENG-2759; No. of Pages 9
ARTICLE IN PRESS
E.A. Kristensen et al. / Ecological Engineering xxx (2013) xxx–xxx
European Environment Agency, 1998. Europe’s Environment – The Second Assessment – An Overview. State of the Environment Report. EEA, Copenhagen, pp.
293.
Feld, C.K., Birk, S., Bradley, D.C., Hering, D., Kail, J., Marzin, A., Melcher, A., Nemitz, D.,
Pedersen, M.L., Pletterbauer, F., Pont, D., Verdonschot, P.F.M., Friberg, N., 2011.
From natural to degraded rivers and back again: a test of restoration ecology
theory and practice. Adv. Ecol. Res. 44, 119–209.
Friberg, N., Kronvang, B., Hansen, H.O., Svendsen, L.M., 1998. Long-term, habitatspecific response of a macroinvertebrate community to river restoration. Aquat.
Conserv. 8, 87–99.
Frissell, C.A., Liss, W.L., Warren, C.E., Hurley, M.D., 1986. A hierarchical framework for
stream habitat classification: viewing streams in a watershed context. Environ.
Manag. 10, 199–214.
Gilvear, D., Bravard, J.P., 1996. Geomorphology of temperate rivers. In: Petts,
G.E., Amoros, C. (Eds.), Fluvial Hydrosystems. Chapman & Hall, London,
pp. 68–97.
Gurnell, A., Petts, G., Hannah, D.M., Smith, B.P.G., Edwards, P.J., Kollmann, J., Ward,
J.V., Tockner, K., 2001. Riparian vegetation and island formation along the gravelbed Fiume Tagliamento, Italy. Earth Surf. Process. Landforms 26, 31–62.
Gurnell, A., Teckner, K., Edwards, P., Petts, G., 2005. Effects of deposited wood on
biocomplexity of river corridors. Fron. Ecol. Environ. 3, 377–382.
Hillman, M., Brierly, G., 2005. A critical review of catchment-scale rehabilitation
programmes. Prog. Phys. Geograp. 29, 50–70.
Hooke, J.M., 2004. Cutoffs galore!: occurrence and causes of multiple cutoffs on a
meandering river. Geomorphology 61, 225–238.
Hutchinson, G.E., 1959. Homage to Santa Rosalia or why are there so many kinds of
animals? Am. Nat. 93, 145–159.
Kasahara, T., Hill, A.R., 2008. Modeling the effects of lowland stream restoration
projects on stream–subsurface water exchange. Ecol. Eng. 32, 310–319.
KMS, 2010. Danmarks Højdemodel – DHM Terræn. National Survey and Cadastre,
pp. 1–10 (In Danish).
Kondolf, G.M., Boulton, A.J., O’Daniel, S., Poole, G.C., Rahel, F.J., Stanley, E.H., Wohl, E.,
Bång, A., Carlstrom, J., Cristoni, C., Huber, H., Koljonen, S., Louhi, P., Nakamura, K.,
2006. Process-based ecological river restoration: visualizing three-dimensional
connectivity and dynamic vectors to recover lost linkages. Ecol. Soc. 11, 1–17.
Kondolf, G.M., Micheli, E.R., 1995. Evaluating stream restoration projects. Environ.
Manage. 19, 1–15.
Kristensen, E.A., Baattrup-Pedersen, A., Jensen, P.N., Wiberg-Larsen, P., Friberg, N.,
2012. Selection, implementation and cost of restorations in lowland streams: a
basis for identifying restoration priorities. Environ. Sci. Policy 23, 1–11.
Kristensen, E.A., Baattrup-Pedersen, A., Thodsen, H., 2011. An evaluation of restoration practises in lowland streams: has the physical integrity been re-created?
Ecol. Eng. 37, 1654–1660.
Kronvang, B., Andersen, I.K., Hoffmann, C.C., Pedersen, M.L., Ovesen, N.B., Andersen,
H.E., 2007. Water exchange and deposition of sediment and phosphorus during
inundation of natural and restored lowland floodplains. Water Air Soil Pollut.
181, 115–121.
Kronvang, B., Audet, J., Baattrup-Pedersen, A., Jensen, H.S., Larsen, S.E., 2012. Phosphorus load to surface water from bank erosionin a Danish lowland river basin.
J. Environ. Qual. 41, 304–313.
Kronvang, B., Svendsen, L.M., Brookes, A., Fisher, K., Møller, B., Ottosen, O., Newson, M., Sear, D., 1998. Restoration of the rivers Brede, Cole and Skerne: a joint
Danish and British EU-LIFE demonstration project, III – channel morphology,
hydrodynamics and transport of sediment and nutrients. Aquat. Conserv. 8,
209–222.
Lake, P.S., 2001. On the maturing of restoration: linking ecological research and
restoration. Ecol. Manage. Res. 2, 110–115.
Larson, M.G., Booth, D.B., Morley, S.A., 2001. Effectiveness of large woody debris in
stream rehabilitation projects in urban basins. Ecol. Eng. 18, 211–226.
Leica Geosystems, 2010. Leica Viva Netrover, Datasheet. Leice Geosystems.
Loomis, J., Kent, P., Strange, L., Fausch, K., Covich, A., 2000. Measuring the total economic value of restoring ecosystem services in an impaired river basin: results
from a contingent valuation survey. Ecol. Econ. 33, 103–117.
Miall, A.D., 1977. Review of braided-river depositional environment. Earth Sci. Rev.
13, 1–62.
Miller, S.W., Budy, P., Schmidt, J.C., 2010. Quantifying macroinvertebrate responses
to in-stream habitat restoration: applications of meta-analysis to river restoration. Res. Ecol. 18, 8–19.
Newson, M.D., Large, A.R.G., 2006. ‘Natural’ rivers, ‘hydromorphological quality’ and
river restoration: a challenging new agenda for applied fluvial geomorphology.
Earth Surf. Process. Landforms 31, 1606–1624.
O’Hare, M.T., Baattrup-Pedersen, A., Nijboer, R., Szoszkiewicz, K., Ferreira, T., 2006.
Macrophyte communities of European streams with altered physical habitat.
Hydrobiologia 566, 197–210.
9
Ovesen, N.B., Iversen, H.L., Larsen, S., Müller-Wohlfeil, D.I., Svendsen, L.M., 2000.
Runoff in Danish water courses (in Danish). Scientific Report from NERI no. 340.
Palmer, M.A., Bernhardt, E.S., Allan, J.D., Lake, P.S., Alexander, G., Brooks, S., Carr,
J., Clayton, S., Dahm, C.N., Follestad Shan, J., Galat, D.L., Loss, S.G., Goodwin, P.,
Hart, D.D., Hassett, B., Jenkinson, R., Kondolf, G.M., Lave, R., Meyr, L.J., O’Donnell,
T.K., Pagano, L., Sudduth, E., 2005. Standards for ecologically successful river
restoration. J. Appl. Ecol. 42, 208–217.
Pedersen, M.L., Andersen, J.M., Nielsen, K., Linnemann, M., 2007a. Restoration of
Skjern River and its valley: project description and general ecological changes
in the project area. Ecol. Eng. 30, 131–144.
Pedersen, M.L., Friberg, N., Skriver, J., Baattrup-Pedersen, A., 2007b. Restoration of
Skjern River and its valley – short-term effects on river habitats, macrophytes
and macroinvertebrates. Ecol. Eng. 30, 145–156.
Pedersen, M.L., Kristensen, E.A., Kronvang, B., Thodsen, H., 2009. Ecological effects
of re-introduction of salmonid spawning gravel in lowland Danish streams. R.
Res. Appl. 25, 626–638, http://dx.doi.org/10.1002/rra.1232.
Petts, G., Maddock, I., Bickerton, M., Ferguson, A.J.D., 1995. Linking hydrology and
ecology: the scientific basis for river management. In: Harper, D.M., Ferguson,
A.J.D. (Eds.), The Ecological Basis for River Management. John Wiley, Chichester,
pp. 1–16.
R Core Team, 2012. A Language and Environment for Statistical Computing. R Core
Team, Vienna, Austria.
Richards, K.S., 1997. Channel morphology and dynamics. In: Thorne, C.R., Hey, R.D.,
Newson, M.D. (Eds.), Applied Fluvial Geomorphology for River Engineering and
Management. Wiley & Sons, p. 376.
Rosgen, D.L., 1996. Applied River Morphology, Wildland Hydrology. Pagosa Springs,
Colorado (USA).
Sala, O.E., Chapin III, F.S., Armesto, J.J., Berlow, E., Bloomfield, J., Dirzo, R., HuberSanwald, E., Huenneke, L.F., Jackson, R.B., Kinzig, A., Leemans, R., Lodge, D.M.,
Mooney, H.A., Oesterheld, M., Poff, N.L., Sykes, M.T., Walker, B.H., Walker, M.,
Wall, D.H., 2000. Global biodiversity scenarios for the year 2100. Science 287,
1770–1774.
Sear, D.A., Briggs, A., Brookes, A., 1998. A priliminary analysis of the morphological adjustment within and downstream of a lowland river subject to river
restoration. Aquat. Conserv. 8, 167–183.
Sear, D.A., Newson, M.D., 2003. Environmental change in river channels: a neglected
element. Towards geomorphological typologies, standards and monitoring. Sci.
Total Environ. 310, 17–23.
Ŝípek, V., Matoušková, M., Dvořák, M., 2009. Comparative analysis of selected hydromorphological assessment methods. Environ. Monit. Assess. 169, 309–319.
Smed, P., 1982. Geomorphological Maps of Denmark. Geograf Forlaget.
Sparks, R.E., 1995. Need for ecosystem management of large rivers and their floodplains. Bioscience 45, 168–182.
Thodsen, H., Pedersen, J.B.T., Svinth, S., Sunesen, S.T., 2006. The influence of climate
change on bed sediment transport in the alluvial River Kongeå, Denmark. In:
Refsgaard, J.C., Højbjerg, A.J. (Eds.), XXIV Nordic Hydrological Conference 2006.
Experiences and Challenges in implementation of the EU Water Framework
Directive, NHP Report. Vingsted, Denmark, pp. 593–600.
Tockner, K., Malard, F., Ward, J.V., 2000. An extension of the flood pulse concept.
Hydrol. Process. 14, 2861–2883.
Van den Brink, P.J., den Besten, P.J., Bij de Vaate, A., Ter Braak, C.J.F., 2009. Principal
response curves technique for the analysis of multivariate biomonitoring time
series. Environ. Monit. Assess. 152, 271–281.
Van den Brink, P.J., Ter Braak, C.J.F., 1999. Principal response curves: analysis of timedependent multivariate responses of biological community to stress. Environ.
Toxicol. Chem. 18, 138–148.
Verdonschot, P.F.M., Niiboer, R.C., 2002. Towards a decision support system for
stream restoration in the Netherlands: an overview of restoration projects and
future needs. Hydrobiologia 478, 131–148.
Vitousek, P.M., Mooney, H.A., Lubchenko, J., Melillo, J.M., 1997. Human domination
of Earth’s ecosystems. Science 277, 494–499.
Vogel, R., 2011. Hydromorphology. J. Water Resour. Plan. Manage. 137, 147–149.
Ward, J.V., Tockner, K., Arscott, D.B., Claret, C., 2002. Riverine landscape diversity.
Freshw. Biol. 47, 517–539.
Wentworth, C.K., 1922. A scale for grade and class terms of clastic sediments. J. Geol.
30, 377–392.
Wilcove, D.S., Rothstein, D., Dubow, J., Phillips, A., Losos, E., 1998. Quantifying threats
to imperiled species in the United States. BioScience 48, 607–615.
Williams, P.B., 2001. River engineering versus river restoration. In: Hayes, D.F. (Ed.),
Proceedings of the 2001 Wetlands Engineering and River Restoration Conference, Reno, Nevada.
Wohl, E., Angermeier, P.L., Bledsoe, B., Kondolf, G.M., MacDonnell, L., Merritt, D.M.,
Palmer, M.A., Poff, N.L., Tarboton, D., 2005. River restoration. Water Resour. Res.
41, 1–12, http://dx.doi.org/10.1029/2005WR003985.
Please cite this article in press as: Kristensen, E.A., et al., 10 years after the largest river restoration project in Northern Europe: Hydromorphological changes on multiple scales in River Skjern. Ecol. Eng. (2013), http://dx.doi.org/10.1016/j.ecoleng.2013.10.001